Arthrogryposis Multiplex (AM), commonly referred to as “Curly Calf Syndrome,” is a genetic defect that has recently been reported in Angus cattle. Based on pedigree examination of affected calves, this genetic defect is determined to have an autosomal recessive mode of inheritance. Due to this recessive inheritance pattern, only calves that are homozygous (i.e., receiving a chromosome with the mutation from both parents) for the mutation causing AM are affected with multiple abnormalities most often including arthrogryposis (contracted or extended limbs with stiffened joints), scoliosis and kyphosis (abnormal curvature of the spine), and muscular hypoplasia (reduced muscle development). Less commonly, the syndrome is associated with mild hydrocephalus caused by inflammation of the brain. Calves are born dead or fail to thrive and die shortly after birth. Classification of normal appearing individuals (e.g., those that are homozygous for the normal allele or heterozygous or carriers of the mutation) is virtually impossible in the absence of planned breeding studies or test matings. Accordingly, there is a need for a test that can reliably identify whether an animal is a heterozygous or a carrier of the mutation.
The American Angus Association® cattle breeders group recently became aware of a small number of calves born dead with bent and twisted spines. Subsequent monitoring of the situation provided further incidents of such calves being born. Reproductive technologies, where certain parents having beneficial traits are used frequently, can result in the observation of unwanted defects introduced in a breeding program. Good tracking of lineage, however, can provide the ability to breed out certain undesirable genes. In this case, extensive breeding and pedigree studies have revealed that AM has an autosomal recessive mode of inheritance. For the AM to be expressed, a calf must have inherited the defective gene from both parents. A calf that expresses the phenotype is “homozygous” for the mutant AM gene, and the parents of such a calf are “heterozygous carriers” for the mutant AM gene (homozygous animals do not survive to reproduce). It is virtually impossible in the absence of planned breeding studies or test matings to classify whether a normal appearing individual is a heterozygous carrier of the mutant AM gene (AM carrier or “AMC”) or is homozygous for the normal allele (AM free or “AMF”). Genetic screening is beneficial in avoiding loss of genetic resources due to culling based only on pedigree.
Because heterozygous individuals appear normal, carriers of the trait cannot be identified by eye, and instead exhaustive and time-consuming familial analysis is required in order to identify potential carrier individuals. There is a need in the art for screens that can identify heterozygous carriers of AM by genetic testing to facilitate a breeding program that eliminates the genetic defect from the population. Such a screen requires an understanding of the genetic basis of the defect, including identification of the causative mutation within the DNA sequence. Disclosed herein is a mutation associated with AM and provided are various genetic tests to determine whether apparently normal individuals carry a defective gene associated with AM. The methods, products and kits provided herein permit testing of individuals to determine whether an individual is a carrier. Individuals that are carriers can be removed from the breeding population, thereby facilitating removal of this genetic defect from the population.
While dramatic culling of suspected carriers would reduce the frequency of the mutation responsible for AM, such culling is long, expensive and can result in unnecessary reduction of beneficial genetic traits, as many of the culled animals would not be carriers of the mutation. Accordingly, there is a need in the art for a diagnostic or genetic screening test to determine whether or not an animal is a carrier of the mutation responsible for AM. Provided herein are materials and methods for screening animals to determine whether an animal is a heterozygous carrier of the mutant allele responsible for AM.